1. Field of the Invention
The present invention relates to a multimedia communicating apparatus as typically represented by an AV (Audio Visual) communicating apparatus such as television telephone or conference system, and more particularly to a multimedia communicating apparatus for communicating multimedia information, such as voice information, video information and data information, in a multiplexed form.
2. Related Background Art
Recently, with start of practical use of communication service through ISDN lines, attention has been focused on AV (Audio Visual) service, such as a television telephone or conference system, using such ISDN lines. For the AV service, CCITT (International Telegraph and Telephone Consultive Committee) has prepared international standardization norms and published their drafts. Service regulations, protocol rules, multimedia multiplexing frame structure rules, animation information encoding schemes, etc. for AV service, by way of example, have been published as CCITT recommendation or recommendation drafts H.221, H.230, H.242, H.261, H.320, etc.
More specifically, H.221 defines the frame structure and exchange of terminal ability in the AV service over B channels with a transfer speed of 64 kbps to 1920 kbps, as well as encoding allocation of BAS (Bit rate Allocation Signal) used in, for example, designating a communication mode. H.230 specifies, as additional information to functions necessary for the AV service, various kinds of control and notice which require synchronization of transferred frames or an urgent response. H.242 defines protocols for ability exchange and communication mode switch between AV terminals using BAS. H.261 specifies animation information encoding/decoding schemes at speeds of p.times.64 kbps (p=1 to 30 channels). Further, H.320 defines a general outline of the AV service system.
When carrying out multimedia communication of video information (animation information), voice information and data information (all user information other than video information and voice information) in accordance with the above CCITT recommendation or recommendation drafts, transfer speeds of the respective media information are determined as follows. The transfer speed of voice information is determined by designating the speed of a voice operation mode, and the transfer speed of data information is determined by designating the speed of a data mode. Then, the transfer speed of video information is the rest resulted by subtracting both the transfer speeds of voice information and data information from the capacity (i.e., the total transfer speed) of effective communication lines available in intercommunication. Accordingly, the transfer speed of video information is variable depending on the transfer speeds of other media information.
The transfer speed of data information is assumed to be adapted for a variety of cases from one transmitting a large quantity of information as required in G3 or G4 facsimile communication, to another transmitting only a small quantity of information as represented by pointing information. Depending on the type of data used, any of LSD (low Speed Data), HSD (High Speed Data), L-MLP (Low Speed Data by Multi-Layer Protocol) and H-MLP (High speed Data by Multi-Layer Protocol) can be selected. Stated otherwise, this type multimedia communicating apparatus is able to effect communication by selecting, at the time of starting data transfer, HSD or H-MLP when a large quantity of information is to be transferred as required in G3 facsimile communication, and LSD or L-MLP when a small quantity of information is to be transferred as represented by pointing information.
In the above conventional multimedia communicating apparatus, however, due consideration has not been paid to the fact that in the case of transmitting and receiving data information by utilizing G4 facsimile communication, for example, the communication from the transmission side to reception side needs a high-speed data channel (e.g., HSD) because a large quantity of information is to be transmitted in this direction, whereas the communication from the reception side to the transmission side only needs a low-speed data channel (e.g., LSD) because a small quantity of control data is transmitted in this direction as protocols of the G4 communication necessary for negotiation with the partner's terminal. This gives rise to a problem that the same data transfer speed, i.e., a data channel of the same capacity, is allocated to both the transmission side and the reception side, resulting in a waste of the channel capacity.
With regards to data information for which abrupt variations in a quantity of data are supposed depending on input conditions by a user, such as encountered in telewriting to transfer information of voice, hand-written characters and/or figures in real time, the CCITT recommendation draft H.221 specifies the data channel variable in speeds over B channels. According to the CCITT recommendation draft H.221, however, it is only possible that the data channel is made variable in speeds over B channels, meaning that video information and data information cannot be multiplexed with each other. Thus, due consideration has not been paid to data information which is transmitted in multiplexed relation to video information and may undergo abrupt variations in a quantity of information. In other words, where data is multiplexed with video information, it is usual to allocate a required data channel at the time of starting transfer of telewriting information and employ the data channel continuously as it is.
The above method has, however, suffered from a problem as follows. When a large capacity is allocated to the data channel, the transfer capacity of the data channel is entirely wasted while telewriting information is not being inputted. On the contrary, when the quantity of telewriting information to be inputted is larger than the allocated capacity of the data channel, a delay in the information transfer may be increased to such an extent that the difference between pictures on the transmission side and the reception side causes users to have some unusual feeling.
FIG. 18 shows basic communication processing procedures as needed when communicating multimedia information such as video information, voice information and data information by utilizing a plurality connections in accordance with the above CCITT recommendation or recommendation drafts, but these procedures have accompanied the following disadvantage. Description will be first made of FIG. 18. Note that the term "connection" is used herein to mean one or more channels.
At first, a multimedia communicating apparatus attempting to start communication (hereinafter referred to as a transmission side communicating apparatus) is initiated to operate, whereupon the first connection is established in a step S701. This step corresponds to a call setting sequence by a D channel in the case of ISDN lines. Then, a step S702 establishes the frame synch through search and detection of FAS and delivery and detection of A bit=0 over the set connection (corresponding to a B channel, an H channel or the like in ISDN). After that establishment of the frame synch, the ability information exchange is performed in a step S703 to judge whether or not a reception side (partner's) communicating apparatus has an ability of setting an additional connection, through the ability information exchange sequence by transmission and reception detection of BAS.
Subsequently, processing goes to a step S704 to judge, based on the ability information in the step S703, whether or not setting of an additional connection is necessary. If the reception side communicating apparatus has an ability of setting an additional connection, then this means that the additional connection is required to be set. Therefore, processing goes to a step S705 to establish (set) the additional connection. Thereafter, a step S706 performs the process of establishing the frame synch, the multiframe synch and the first channel synch through search and detection of FAS and utilization of A bit over the additional connection.
Then, processing returns to the step S704 to judge again whether or not setting of an additional connection is necessary. If the step S704 judges no necessity of setting the additional connection as a result of that the reception side communicating apparatus has lost the ability of setting an additional connection, then a step S707 switches a transmission mode and a reception mode through transmission and reception detection of BAS commands. Next, a step S708 carries out multiplexing communication of the multimedia information in the transmission and reception modes established in the step S708, followed by ending the processing operation.
Alternatively, the transmission and reception mode switch sequence executed in the above step S707 using BAS commands may be performed immediately after the execution of the step S703, or each time the connection is added in the step S705.
It should be appreciated that the above CCITT recommendation (or recommendation drafts) includes no particular provisions about whether initiating the operation to establish an additional connection is to be carried out in the transmission side communicating apparatus or the reception side communicating apparatus, and about what is a concrete trigger to be used for that initiation. Moreover, no particular provisions are included therein also about how to handle the situation if the setting of an additional connection could not be established by the call control procedures for the D channel in ISDN, for example.
In the above conventional multimedia communicating apparatus shown in FIG. 18, however, since the additional connection is set unconditionally after the step S704 has judged, based on the ability information due to the ability information exchange sequence in the step S703, that the reception side communicating apparatus also has an ability of setting an additional connection, the user is not required to perform the specific operation directed at the setting of an additional connection, but to the contrary, the additional connection is automatically set more than necessary, which results in a problem of wasteful buildup of the line charge.
Meanwhile, there has accompanied a problem of making the operation troublesome in the communicating apparatus of the opposite type that the setting of an additional connection must be always initiated upon the manual operation of the user.
In the communicating apparatus that the same operation is carried out simply for all the partners (reception side communicating apparatus), a great deal of waste has been experienced in economy because the additional connection is set to be of no use depending on only the partner's ability of setting plural additional connections, or because not only those partners giving rise to higher line charges with a long distance like oversea communication, but also those partners giving rise to lower line charges with a short distance are all handled equally.
Further, when the additional connection could not be set eventually after initiating the operation to set an additional connection, the operation of retrying to set an additional connection must be manually initiated by the user. This raises a problem that the need of such operation causes the user to feel troublesome, or that since the intercommunication can be eventually effected even with no additional connections, the communication is completed without retrying to set an additional connection.
Moreover, even when the cause of preventing the setting of an additional connection is detected by the reception side transmitting apparatus, the situation is handled by the reception side transmitting apparatus only retrying the procedures of setting of an additional connection for the reception side transmitting apparatus, or by only the manual operation by the user. This raises another problem that the procedures of setting an additional connection are uselessly initiated for retry and the additional connection cannot be set again even with the initiation retried.